Monensin and essential oils can be beneficial to lactating cows on grazing systems adopting high grain feeding. We evaluated the effect of a microencapsulated blend of capsaicin, carvacrol, cinnamaldehyde, and eugenol (CEO. Four g/d) relative to monensin (MON. 300 mg/d) or control (CTL) on lactation performance, pasture intake, total-tract apparent digestibility, rumen microbial yield, and rumination of grazing Holsteins. After a 14-d standardization period (Covariate), 60 cows (183 ± 95 DIM) were blocked by parity and milk yield and assigned to a treatment for 28 d with response evaluated on wk 4. Pre-planned contrasts were: C1) CTL vs. CEO and C2) CEO vs. MON. Capsules with treatments were given orally 1×/d. Cows were milked 2×/d and locked-fed 5.54 kg/d of corn silage DM (7.9% CP, 55.1% NDF) and 2.70 kg of concentrate DM (16.3% CP, 14.7% NDF) at 0230, 1130, 1430, and 1700 h. Paddocks of ryegrass-white clover (17.6% CP, 49.9% NDF) were grazed for 324 ± 53.7 min/d and pre- and post-grazing heights of 12.2 cm and 10.1 cm, respectively. Cows were orally dosed from d 14 to 28 with Cr₂O₃ to estimate fecal production. Pasture was harvested with a rumen fistulated cow allowed to graze for 50 min after ruminal evacuation. The in situ content of iNDF in feeds (244 h) estimated pasture intake and total-tract digestibility. The allantoin to creatinine ratio of urine spot samples estimated rumen microbial yield. Rumination was recorded automatically with neck collars (SCR, Israel). Treatments had no effect on pasture intake (7.22 kg/d), milk yield (36.6 kg/d), solids yield and concentration, BW (679 kg), BCS (2.9), and rumination activity (546 min/d) (P ≥ 0.28 for C1 and C2). The CEO reduced the concentration of urea-N in milk (P ≤ 0.03 for C1 and C2) and plasma (P < 0.01 for C1 and C2). The NDF digestibility was reduced by CEO (P ≤ 0.03 for C1 and C2) and the urinary allantoin to creatinine ratio tended to be reduced by MON (P = 0.10 for C2). Lactation performance and pasture intake were not affected by MON and CEO.